In motor vehicles, even under a change of the same operation condition (viz., change in operation condition induced by an amount of depression of an accelerator pedal and/or change in running condition induced by a vehicle speed), an acceleration obtained is largely changed in accordance with an output torque characteristic of a driving power source, and thus, actually, it is impossible for a driver to get or enjoy an acceleration that is desired by him or her in accordance with a change of the operation condition (viz., change in operation condition induced by an amount of depression of the accelerator pedal and/or change in running condition induced by the vehicle speed).
The reason is that output torque characteristics of most power sources do not correspond to a change of the required acceleration expected by the driver in response to an operation handling, and thus, it tends to occur that the driver is given such a dissatisfaction that a vehicle running performance (viz., sense of acceleration) is not sufficient and a delicate driving manipulation is not effected due to an excessive torque.
Thus, in common motor vehicles having an engine mounted thereon, a transmission for adjusting a torque from the power source is arranged at an output side of the power source for obtaining an acceleration as expected by the driver.
Also in electric motor vehicles having an electric motor installed thereon as a power source, since the electric motor, like in the above-mentioned engine, does not bring about an expected desired acceleration due to the characteristic of the output torque from the motor, it tends to occur that the driver is given such a dissatisfaction that a vehicle running performance (viz., sense of acceleration) is not sufficient and a delicate driving to manipulation is not effected due to an excessive torque.
However, if, in the electric motor vehicles using the electric motor as the driving power source, a transmission is arranged at an output side of the motor for intending to get the desired acceleration, the transmission becomes a factor for increasing a friction loss, and besides this, since control of the transmission consumes energy, a travel distance (viz., mileage per one charge) of the vehicle becomes shorter, which is a serious problem.
Accordingly, in case of electric motor vehicles, the above-mentioned ordinary solution of mounting a transmission at the output side of an electric motor can not be adopted.
In case of electric motor motors, the response of output torque is easily controlled unlike in case of an internal combustion engine or the like, and thus, the inventors have considered that if a sense of acceleration is suitably adjusted by controlling the torque response, the driver may be given a satisfaction.
As a technology to control the torque response of an electric motor, there has been proposed only one technique in which as is described in Patent Document 1, since an electric motor generates a large torque at a lower speed and a torsional vibration is inevitably produced in a motor driving system, the torque response is so controlled as to suppress generation of the torsional vibration in the motor driving system.
However, the proposed technique disclosed in Patent Document 1 is to control the torque response of the electric motor in a manner to suppress generation of the torsional vibration in the motor driving system, which is not a torque responsive control technique for providing the driver with a sense of acceleration that is desired by him or her in accordance with a change of an operation condition of the vehicle.
Accordingly, the proposed technique described in Patent Document 1 does not solve the above-mentioned problems in which a driver is given such a dissatisfaction that a vehicle running condition (viz., sense of acceleration) is not sufficient and a delicate driving manipulation is not effected due to an excessive torque.